Particulate filter and method for control

ABSTRACT

An exhaust treatment system comprises a filter device in communication with the engine and configured to receive exhaust gas therefrom. The filter device comprises a canister including an inlet, a filter structure having an upstream, inlet end, a downstream, outlet end, and a series of filtering flow passages. A center zone conduit is in sealing, fluid contact with the downstream, outlet end of the filter structure to thereby define a center flow zone and perimeter flow zone. A flow control valve assembly is disposed in the center zone conduit. A controller is in signal communication with the flow control valve and a temperature sensor and monitors a temperature profile of the filter structure wherein, upon a determination that the temperature of the center flow zone of the filter structure is above a predetermined level, the controller drives the flow control valve assembly to a closed position.

FIELD OF THE INVENTION

The subject invention relates to particulate filters suitable for the removal of particulates in the exhaust gas of internal combustion engines and, in particular, a system that controls the flow of exhaust gas through a particulate filter when the flow of the exhaust gas is reduced to a rate that induces a temperature increase therein.

BACKGROUND

Exhaust gas emitted from an internal combustion (IC) engine is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (CO), unburned hydrocarbons (HC) and oxides of nitrogen (NOx) as well as condensed phase materials (liquids and solids) that constitute particulate matter (PM). Catalyst compositions, that are typically disposed on catalyst supports or substrates, are provided in an engine exhaust system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.

An exhaust treatment technology in use for PM reduction is the particulate filter (PF) device. There are several known filter structures used in PF devices such as ceramic honeycomb wall flow filters, wound or packed fiber filters, open cell foam filters, sintered metal filters, sintered metal foams, etc. Ceramic honeycomb wall flow filters have experienced significant acceptance in automotive applications. One potential drawback to the ceramic filter (and any filter with significant particulate loading) is its operational limits at higher temperatures. A mode of operation which can affect the performance of the particulate filter is a sudden reduction of exhaust flow, with high levels of oxygen, through the PF device during a regeneration event in which the collected particulate matter is being oxidized. The regeneration event is used to clean the particulate filter and to reduce backpressure experienced by the internal combustion engine. During the regeneration event, temperatures are high and a sudden reduction in exhaust flow through the particulate filter can reduce heat transfer from the filter, especially near the center portion where heat transfer is low, causing durability reducing temperature excursions.

Accordingly, it is desirable to provide a system to control the flow of exhaust gas through the PF device, particularly the center portion, during high temperature events, such as regeneration, to avoid performance reducing temperature excursions.

SUMMARY OF THE INVENTION

In an exemplary embodiment, an exhaust treatment system for an internal combustion engine comprises a particulate filter device in fluid communication with the internal combustion engine and configured to receive exhaust gas therefrom. The particulate filter device comprises a canister that includes an inlet for receipt of the exhaust gas, a filter structure having an upstream, inlet end, a downstream, outlet end, and a series of filtering flow passages extending therebetween. A center zone conduit is in sealing, fluid contact with the downstream, outlet end of the filter structure to thereby define the filter structure into a center flow zone and perimeter flow zone. A flow control valve assembly is disposed in the center zone conduit and is operable between an open and a closed position. A temperature and a controller is in signal communication with the flow control valve and the temperature sensor and is configured to monitor a temperature profile of the filter structure wherein, upon a determination that the temperature of the center flow zone of the filter structure has risen above a predetermined level, the controller will drive the flow control valve assembly to a closed position to thereby stop the flow of exhaust gas through the center flow zone of the filter and reduce the temperature thereof.

In another exemplary embodiment, a method for controlling the temperature of a particulate filter in an exhaust treatment system for an internal combustion engine comprising the steps of placing a particulate filter device in fluid communication with the internal combustion engine and configuring it to receive exhaust gas therefrom. The device comprises a canister that includes an inlet for receipt of the exhaust gas and a filter structure having an upstream, inlet end, a downstream, outlet end, and a series of filtering flow passages extending therebetween. The steps further include locating a center zone conduit in sealing, fluid contact with the downstream, outlet end of the filter structure to thereby define the filter structure into a center flow zone and perimeter flow zone; positioning a flow control valve assembly in the center zone conduit that is operable between an open and a closed position; locating a temperature sensor at the downstream, outlet end of the filter structure; and operating a controller to monitor a temperature profile of the filter structure wherein, upon determining that the temperature of the center flow zone of the filter structure has risen above a predetermined level, the controller will drive the flow control valve assembly to a closed position to thereby stop the flow of exhaust gas through the center flow zone of the filter and reduce the temperature thereof.

In yet another exemplary embodiment, an exhaust treatment system for an internal combustion engine comprises a particulate filter device in fluid communication with the internal combustion engine and configured to receive exhaust gas therefrom. The particulate filter device comprises a canister that includes an inlet for receipt of the exhaust gas, a filter structure having an upstream, inlet end, a downstream, outlet end, and a series of filtering flow passages extending therebetween. A center zone conduit is in sealing, fluid contact with an end of the filter structure to thereby define the filter structure into a center flow zone and perimeter flow zone. A flow control valve assembly is disposed in the center zone conduit and is operable between an open and a closed position. A temperature and a controller is in signal communication with the flow control valve and the temperature sensor and is configured to monitor a temperature profile of the filter structure wherein, upon a determination that the temperature of the center flow zone of the filter structure has risen above a predetermined level, the controller will drive the flow control valve assembly to a closed position to thereby stop the flow of exhaust gas through the center flow zone of the filter and reduce the temperature thereof.

The above features and advantages and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only, in the following detailed description of the embodiments, the detailed description referring to the drawings in which:

FIG. 1 is a schematic diagram of an exhaust gas treatment system for an internal combustion engine embodying features of the invention;

FIG. 2 is a schematic view of a particulate filter device for an exhaust treatment system of an internal combustion engine, embodying features of the invention; and

FIG. 3 is a schematic sectional view, taken along line 3-3 of FIG. 2.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that, throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term vehicle is not limited to just an automobile, truck, van or sport utility vehicle, but includes any self-propelled or towed conveyance suitable for transporting a burden.

Referring now to FIG. 1, exemplary embodiments of the present disclosure are directed to an exhaust gas treatment system 10 that reduces various constituents in exhaust gas 11 generated by an internal combustion engine 12 of the type that may commonly be applied in automotive applications. It is appreciated that the exhaust treatment system 10 described herein may be utilized with various engine systems that may include, for example, but are not limited to, diesel engines and gasoline engines.

Combustion air 13 is drawn into the engine 12 and mixed with fuel (not shown). The air/fuel mixture is combusted and is expelled as exhaust gas 11 through exhaust conduits 16 that are in fluid communication with the exhaust treatment system 10. The exhaust treatment system 10 generally includes one or more exhaust conduit segments extending between one or more exhaust treatment devices. The exhaust treatment devices may include an oxidation catalyst device (OC) 20, a selective catalyst reduction device (SCR) 22, and a particulate filter (PF) device 24. Other configurations are contemplated.

Referring now to FIG. 2, with continuing reference to FIG. 1, a PF device 24 comprises a filter structure such as a ceramic wall-flow filter 26 that is supported by an insulating mat 28 in a rigid canister 30. The rigid canister 30 is typically constructed of stainless steel or other durable, high temperature material and includes an inlet 32 in fluid communication with exhaust conduit 16 for receipt of exhaust gas 11. The filter structure 26 includes an upstream, inlet end 34, a downstream, outlet end 36, and a series of filtering flow passages (not shown) extending therethrough. Exhaust gas 11 entering the rigid canister 30 through inlet 32 flows through the filter structure 26 from the upstream, inlet end 34 through the filtering passages, where it deposits particulate matter suspended therein, and exits the downstream outlet end 36.

Due to various flow characteristics of the exhaust gas 11 caused by the sometimes conical shaped inlet of the canister 30, as well as convective heat transfer from the outside surface 38 of the rigid canister 30, the temperature profile of the ceramic wall-flow filter 26 varies across its cross-section with higher temperatures being measured towards a center zone 40, FIG. 3, of the filter and lower temperatures are measured near a perimeter zone 42. This temperature variation or differential may be pronounced during regeneration of the PF device 24 when exhaust gas 11 has been heated prior to entering the ceramic wall-flow filter 26 in order to initiate combustion of the trapped particulates that are stored thereon. During a regeneration event, heat transfer from the outside surface 38 of the rigid canister 30 (i.e. radiant, convection and conduction), as well as through the flow mechanism of the exhaust gas 11 passing through the PF device, is relied on to maintain the temperature of the filter 26 within an acceptable range of operation.

Should the flow of exhaust gas 11 be reduced by an event such as a sudden reduction of the engine speed to idle temperatures in the filter 26, especially in the center flow zone 40, may exceed those which are desirable for satisfactory performance of the PF device 24. Such an excessive thermal gradient may cause the ceramic wall-flow filter 26 to crack due to uneven expansion of the material. To address temperature excursions of the center flow zone 40 of the ceramic wall-flow filter 26, a center zone conduit 44 is in sealing, fluid contact with the downstream, outlet end 36 of the filter in a configuration that divides the outlet end of the filter into the aforementioned center flow zone 40 and a perimeter flow zone 42. The upstream, inlet end 43 of the center zone conduit 44 may be inset into the filter media FIG. 2, or a ring or cup seal (not shown) may be located about the perimeter of the upstream, inlet end 43 and configured define a seal between the center zone conduit 44 and the downstream, outlet end 36 of the ceramic wall-flow filter 26. The seal may be constructed from a high temperature flexible material such as graphite or other similar material that can compress with the expansion of the particulate filter and the cup. It should be noted that the manner of sealing may have any suitable structure that enables system 10 to function as described herein.

Exhaust gas 11 flowing through the ceramic wall-flow filter 26 from the upstream, inlet end 34 to the downstream, outlet end 36 exits the filter from either i) the center zone 40 and into the center zone conduit 44 for transport further downstream in the exhaust gas treatment system 10 or ii) the perimeter zone 42 and back into the canister 30 for transport further downstream in the exhaust gas treatment system 10. A flow control valve assembly 46 is disposed in the center zone conduit 44 and is operable between an open and a closed position. Temperature sensors 47 may be positioned at one or more positions across the downstream, outlet end 36 of the filter 26, or within the filter, FIG. 1, to allow a controller 48 in signal communication therewith to monitor the temperature profile of the filter. Upon a determination that the temperature of the exhaust flow in center zone 40 of the ceramic wall-flow filter 26 has risen above a predetermined level, the controller 48 will drive the flow control valve assembly 46 to a closed position to thereby stop or restrict the flow of exhaust gas 11 through the center zone 40 of the filter 26. While a reduction or a complete cessation of exhaust flow may appear counterintuitive, such an action reduces or eliminates the introduction of oxygen to the center zone 40 of the filter 26 resulting in extinguishing of the regeneration event and a rapid reduction of the temperature in that portion of the ceramic wall-flow filter 26.

Once the temperature of the center zone 40 has dropped below a predetermined level, as measured by the temperature sensor(s) 47, the controller 48 will drive the flow control valve assembly 46 to an open position to thereby resume the flow of exhaust gas 11 through the center zone 40 of the filter 26 of the PF device 24. It should be noted that in an exemplary embodiment, the exhaust flow 11 through the center zone conduit 44 is rejoined with the exhaust flow 11 from the perimeter zone prior to exiting the rigid canister 30 at canister outlet 50. In an exemplary embodiment, the flow control valve assembly 46 may include a plurality of valves positioned in the center zone conduit 44 and the perimeter zone 42. In certain cases it may be useful to restrict the flow of exhaust gas 11 through the perimeter zone 42 so as to increase the flow through, and therefore the heat transfer out of, the center zone 40 of the filter 26.

While the invention has been described with reference to a center zone conduit 44 and flow control valve assembly 46 located in downstream relationship to a ceramic wall-flow filter 26 disposed in a PF device 24, it is contemplated that the flow control may take place upstream of the filter in embodiments of the invention. In such a variation of the invention it is contemplated that the center zone conduit 44 and flow control valve assembly 46 will be located in a similar relationship to the upstream, inlet end 34 of the filter 26 and will regulate exhaust gas flow 11 through the filter 26 in a similar manner to that already described.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation of material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the application. 

What is claimed is:
 1. An exhaust treatment system for an internal combustion engine comprising: a particulate filter device in fluid communication with the internal combustion engine and configured to receive exhaust gas therefrom, comprising: a canister that includes an inlet for receipt of the exhaust gas; a filter structure having an upstream, inlet end, a downstream, outlet end, and a series of filtering flow passages extending therebetween; a center zone conduit in sealing, fluid contact with the downstream, outlet end of the filter structure to thereby define the filter structure into a center flow zone and perimeter flow zone; a flow control valve assembly disposed in the center zone conduit and operable between an open and a closed position; a temperature sensor; and a controller in signal communication with the flow control valve and the temperature sensor and configured to monitor a temperature profile of the filter structure wherein, upon a determination that the temperature of the center flow zone of the filter structure has risen above a predetermined level, the controller will drive the flow control valve assembly to a closed position to thereby stop the flow of exhaust gas through the center flow zone of the filter and reduce the temperature thereof.
 2. The exhaust treatment system of claim 1, the particulate filter device further comprises a ceramic wall-flow filter supported by an insulating mat and disposed in a rigid canister.
 3. The exhaust treatment system of claim 1, further comprising one or more of an oxidation catalyst device and a selective catalyst reduction device.
 4. The exhaust treatment system of claim 1, wherein, upon a determination that the temperature of the center flow zone of the filter structure has dropped below a predetermined level, the controller will drive the flow control valve assembly to an open position to thereby allow the flow of exhaust gas through the center flow zone of the filter.
 5. A method for controlling the temperature of a particulate filter in an exhaust treatment system for an internal combustion engine comprising the steps of: placing a particulate filter device in fluid communication with the internal combustion engine and configuring it to receive exhaust gas therefrom, the device comprising: a canister that includes an inlet for receipt of the exhaust gas and a filter structure having an upstream, inlet end, a downstream, outlet end, and a series of filtering flow passages extending therebetween; locating a center zone conduit in sealing, fluid contact with the downstream, outlet end of the filter structure to thereby define the filter structure into a center flow zone and perimeter flow zone; positioning a flow control valve assembly in the center zone conduit that is operable between an open and a closed position; locating a temperature sensor at the downstream, outlet end of the filter structure; and operating a controller to monitor a temperature profile of the filter structure wherein, upon determining that the temperature of the center flow zone of the filter structure has risen above a predetermined level, the controller will drive the flow control valve assembly to a closed position to thereby stop the flow of exhaust gas through the center flow zone of the filter and reduce the temperature thereof.
 6. The method of claim 5, further comprising the steps of, operating the controller to monitor the temperature profile of the filter structure wherein upon a determination that the temperature of the center flow zone of the filter structure has dropped below a predetermined level, the controller will drive the flow control valve assembly to an open position to thereby allow the flow of exhaust gas through the center flow zone of the filter.
 7. An exhaust treatment system for an internal combustion engine comprising: a particulate filter device in fluid communication with the internal combustion engine and configured to receive exhaust gas therefrom, comprising: a canister that includes an inlet for receipt of the exhaust gas; a filter structure having an upstream, inlet end, a downstream, outlet end, and a series of filtering flow passages extending therebetween; a center zone conduit in sealing, fluid contact with an end of the filter structure to thereby define the filter structure into a center flow zone and perimeter flow zone; a flow control valve assembly disposed in the center zone conduit and operable between an open and a closed position; a temperature sensor; and a controller in signal communication with the flow control valve and the temperature sensor and configured to monitor a temperature profile of the filter structure wherein, upon a determination that the temperature of the center flow zone of the filter structure has risen above a predetermined level, the controller will drive the flow control valve assembly to a closed position to thereby stop the flow of exhaust gas through the center flow zone of the filter and reduce the temperature thereof.
 8. The exhaust treatment system of claim 7, wherein, upon a determination that the temperature of the center flow zone of the filter structure has dropped below a predetermined level, the controller will drive the flow control valve assembly to an open position to thereby allow the flow of exhaust gas through the center flow zone of the filter. 